Propylene oxide is an important industrial chemical intermediate. Propylene oxide can be produced by direct oxidation of propylene with oxygen and hydrogen in a solvent in the presence of a catalyst (U.S. Pat. Nos. 7,138,535; 7,238,817; 7,279,145; and 5,973,171).
The copending application Ser. No. 11/728,098, filed on Mar. 23, 2007, teaches that a propylene oxide reaction product mixture stream comprising propylene oxide, solvent, propylene, propane, and various oxygenated materials is passed from a propylene oxide producing reaction unit to a flash separator wherein the mixture is flashed to form separate vapor and liquid phases. From the separator a vapor fraction is passed to a propylene oxide absorber wherein propylene oxide is absorbed into an absorption methanol/water liquid. The overhead vapors from the absorber are recycled to the propylene oxide reaction system with a small portion being sent to a vent recovery system.
Propylene oxide produced in the direct oxidation often further reacts with the solvent such as water and an alcohol in the reactor to form byproducts such as propylene glycol, dipropylene glycol, and propylene glycol ethers. This invention reduces the formation of such byproducts.